Multi-parallel magnetic-field cancellation type transformer

ABSTRACT

A multi-parallel magnetic-filed cancellation type transformer includes a plurality of coils which generate magnetic flux during energization and a core having a plurality of magnetic leg portions on which the coils are wound, and bases for fixing the magnetic leg portions. The plurality of coils are wound on the magnetic leg portions in such a manner that the magnetic flux generated from the coils are formed in the directions opposite to each other. A plurality of closed magnetic circuits of the magnetic flux are formed at the magnetic leg portions and the bases. The magnetic resistance of the closed magnetic circuits is homogeneous. Accordingly, the transformer can reduce the size thereof, and prevent the deterioration of electric power conversion efficiency.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a divisional application of U.S. patent application Ser. No.12/320,106, filed on Jan. 16, 2009, which claims foreign prioritybenefit under Title 35, United States Code, §119 (V1)-(d), of JapanesePatent Application No. 2008-006438A, filed on Jan. 16, 2008 in the JapanPatent Office. The disclosures of the prior applications are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multi-parallel magnetic-fieldcancellation type transformer for converting a voltage and an electricpower conversion circuit including the transformer.

2. Description of the Related Art

Heretofore, there is known an electric power conversion circuit, aso-called DC-DC converter, which converts electric power by steppingup/down an input voltage (for example, JP2006-149054A discloses theDC-DC converter).

The conventional DC-DC converter disclosed in JP2006-149054A includes atransformer in which a primary coil and a secondary coil are connectedto each other, and an inductor applied for varying a step-up/down rateand disposed between the transformer and an input-output terminal towhich a voltage is applied. The conventional DC-DC converter cansuccessively step up/down the voltage and reduce the size of theinductor, which leads to the downsized DC-DC converter.

However, according to the conventional DC-DC converter, if thestep-up/down rate is equal to or greater than two times, thesimultaneous ON state of a plurality of switching elements connected tothe coils of the transformer causes a ripple current to increase. Theripple current is a pulsation component to be superimposed on a directcurrent flowing through the inductor applied for varying thestep-up/down rate. Accordingly, the conventional DC-DC converter cannotsmooth out the pulsation (variation) of the ripple current withoutincreasing the body dimension (size) of a capacitor or an inductor.Therefore, it is difficult to reduce the size of such passive elementsas capacitors and inductors and reduce the size of the DC-DC converterdisclosed in JP2006-149054.

Further, according to the conventional DC-DC converter, when thestep-up/down rate is equal to or greater than two times, an increase ofthe ripple current leads to the deterioration of electric powerconversion efficiency.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a multi-parallelmagnetic-filed cancellation type transformer and an electric powerconversion circuit including the transformer, which can reduce the sizeof the transformer and prevent the deterioration of the electric powerconversion efficiency.

A multi-parallel magnetic-filed cancellation type transformer comprises:a plurality of coils, each of which generates magnetic flux whenenergized; and a core which includes a plurality of magnetic legportions about which the coils are wound, and a base for fixing theplurality of magnetic leg portions, wherein the direction of themagnetic flux generated from the plurality of coils are opposite to eachother in any couple selected from among the pieces of magnetic flux, sothat the magnetic flux is cancelled out with each other, and wherein aplurality of closed magnetic circuits of the magnetic flux are formed inthe magnetic leg portions and the bases, and a magnetic resistance of atleast the smallest closed magnetic circuit from among the plurality ofclosed magnetic circuits is homogeneous.

According to the multi-parallel magnetic-filed cancellation typetransformer, the amount of magnetic flux which constitutes a closedmagnetic circuit is homogeneous, so that the transformers can cancel outthe direct current magnetic flux generated from each coil at theelectric power conversion. Accordingly, if the number of the coilsdisposed in parallel increases, the transformers can prevent themagnetic saturation of the core, and reduce the size thereof and a coreloss.

According to the multi-parallel magnetic-filed cancellation typetransformer, wherein the plurality of coils which generate the closedmagnetic circuits are connected in parallel with each other.

According to the multi-parallel magnetic-filed cancellation typetransformer, the plurality of coils are connected in parallel, so thatthe amount of current flowing through the coils can be reduced.Accordingly, since the thickness of the coils is reduced, thetransformer can improve the latitude of design of the coils and enhancespace efficiency.

According to the multi-parallel magnetic-filed cancellation typetransformer, wherein the magnetic path length of the closed magneticcircuits is homogeneous.

The multi-parallel magnetic-filed cancellation type transformer isconstructed to equalize the magnetic path length in order to obtain thehomogeneous magnetic resistance of the closed magnetic circuits, wherebybalancing the magnetic flux density distribution and preventing themagnetic saturation. In this case, the magnetic resistance Rm iscalculated as follows; Rm=1/μ·L/A (magnetic permeability: μ, magneticpath length: L, cross section of magnetic path: A). If the product ofthe magnetic permeability and the cross section of magnetic path isconstant in the formula described above, the homogeneous magneticresistance can be obtained in accordance with the equal magnetic pathlength.

According to the multi-parallel magnetic-filed cancellation typetransformer, wherein the base of the core is formed in a flat circularshape, and the magnetic leg portions of the core are extended from thecenter of the base to the circumference and disposed at regularintervals on the circumference.

According to the multi-parallel magnetic-filed cancellation typetransformer, the magnetic leg portions are formed at regular intervalson the circumference of the base, whereby equalizing the magnetic pathlength of each closed magnetic circuit and obtaining the homogeneousmagnetic resistance. Accordingly, the transformer can prevent theimbalance of the magnetic flux density distribution and the magneticsaturation.

According to the multi-parallel magnetic-filed cancellation typetransformer, the base of the core is formed in a regular polygonalshape, and the magnetic leg portions of the core are extended from thecenter of the core to the sides and disposed at regular intervals on thesides.

According to the multi-parallel magnetic-filed cancellation typetransformer, the magnetic leg portions are formed at regular intervalson the sides of the base, whereby equalizing the magnetic path length ofeach closed magnetic circuit and obtaining the homogeneous magneticresistance. Accordingly, the transformer can prevent the imbalance ofthe magnetic flux density distribution and the magnetic saturation.

According to the multi-parallel magnetic-filed cancellation typetransformer, two bases of the core are formed in a flat circular shapeor a regular triangle and disposed in parallel with each other, and theplurality of magnetic leg portions of the core are formed in acylindrical shape and disposed vertically to the two bases and atregular intervals apart.

According to the multi-parallel magnetic-filed cancellation typetransformer, the two bases are respectively formed on a plane anddisposed in parallel with each other, and the plurality of magnetic legportions are formed in a cylindrical shape and disposed vertically tothe two bases, whereby equalizing the magnetic path length of eachclosed magnetic circuit and obtaining the homogeneous magneticresistance. Accordingly, the transformer can prevent the imbalance ofthe magnetic flux density distribution and the magnetic saturation.

According to the multi-parallel magnetic-filed cancellation typetransformer, two bases of the core are respectively formed on a planeand disposed in parallel with each other, and a plurality of magneticleg portions of the core are formed in a cylindrical shape and disposedvertically to the planes and at regular intervals apart. Further, on oneplane, the base is constituted by only a part where one ends of themagnetic leg portions are mutually joined, and on the other plane, thebase is constituted by only a part where the other ends of the magneticleg portions are mutually joined.

According to the multi-parallel magnetic-filed cancellation typetransformer, the two bases of the core are respectively formed on theplanes and disposed in parallel, and a plurality of magnetic legportions of the core are formed in the cylindrical shape and disposedvertically to the planes and at regular intervals apart, wherebyequalizing the magnetic path length of each closed magnetic circuit andobtaining the homogeneous magnetic resistance. Accordingly, thetransformer can prevent the imbalance of the magnetic flux densitydistribution and the magnetic saturation. Further, according to thetransformer of multi-parallel magnetic-filed cancellation type, on oneplane, the base is constituted of only a part where one ends of themagnetic leg portions are mutually joined, and on the other plane, thebase is constituted of only a part where the other ends of the magneticleg portions are mutually joined, whereby providing a lightweight core,compared with a base having a flat plane.

A multi-parallel magnetic-filed cancellation type transformer comprises:a plurality of coils, each of which generates magnetic flux whenenergized; and a core which includes three magnetic leg portions aboutwhich the coils are wound, and a base for fixing the three magnetic legportions, wherein the three magnetic leg portions are disposed atregular intervals in one direction, and the direction of the magneticflux generated from the plurality of coils wound on the three magneticleg portions are opposite to each other in any couple selected fromamong the pieces of magnetic flux, so that the magnetic flux iscancelled out with each other, and there is a gap in the magnetic legportion disposed at the center between the three magnetic leg portions,and wherein a plurality of closed magnetic circuits of the magnetic fluxare formed in the magnetic leg portions and the base, and a magneticresistance of at least the smallest closed magnetic circuit from amongthe plurality of closed magnetic circuits is homogeneous.

According to the multi-parallel magnetic-filed cancellation typetransformer, the direction of the magnetic flux generated from theplurality of coils wound on the three magnetic leg portions are oppositeto each other in any couple selected from among the pieces of magneticflux, so that the magnetic flux is cancelled out with each other.Further, the gap at the magnetic leg portion formed at the centerbetween the three magnetic leg portions is provided in order to equalizemagnetic resistance generated at the three magnetic leg portions and thebase which fixes the three magnetic leg portions. Accordingly, thetransformer can adjust the amount of magnetic flux which constitutes aclosed magnetic circuit, so that the transformer can cancel out thedirect current magnetic flux generated from each coil at the electricpower conversion. Consequently, the transformer can prevent theimbalance of the magnetic flux density distribution and the magneticsaturation.

An electric power conversion circuit which converts an electric power bytransforming an input voltage and includes a first input-outputconnecting terminal and a second input-output terminal comprises: amulti-parallel magnetic-filed cancellation type transformer; an inductorwhose one end is connected to a positive electrode of the firstinput-output connecting terminal, and whose other end is connected to acommon terminal connecting to the plurality of coils of themulti-parallel magnetic-filed cancellation type transformer; a pluralityof first energization control elements whose one ends are connected tothe plurality of coils respectively, and whose other ends are connectedto a negative electrode of the first input-output connecting terminal;and a plurality of second energization control elements whose one endsare connected to the plurality of coils respectively, and whose otherends are connected to a positive electrode of the second input-outputconnecting terminal.

According to the electric power conversion circuit, the first and secondenergization control elements can control the timing for energizing theinductor and the multi-parallel magnetic-field cancellation typetransformer and a current flow in the circuit, and the multi-parallelmagnetic-field cancellation type transformer can transform a voltage(step up/down a voltage) and convert electric power.

An electric power conversion circuit which converts an electric power bytransforming an input voltage and includes a first input-outputconnecting terminal and a second input-output terminal, the electricpower conversion circuit comprises: a multi-parallel magnetic-filedcancellation type transformer; a plurality of first energization controlelements whose one ends are connected to the plurality of coilsrespectively, and whose other ends are connected to a negative electrodeof the first input-output connecting terminal; and a plurality of secondenergization control elements whose one ends are connected to theplurality of coils respectively, and whose other ends are connected to apositive electrode of the second input-output connecting terminal.According to the electric power conversion circuit, wherein themulti-parallel magnetic-filed cancellation type transformer furthercomprises: a plurality of coils, each of which generates magnetic fluxwhen energized; and a core including three magnetic leg portions aboutwhich the coils are wound, and a base for fixing the three magnetic legportions, wherein the three magnetic leg portions are disposed atregular intervals in one direction, and the direction of the magneticflux generated from the plurality of coils wound on the three magneticleg portions is opposite to each other in any couple selected from amongthe pieces of magnetic flux, so that the magnetic flux is cancelled outwith each other, and there is a gap at the magnetic leg portion formedat the center between the three magnetic leg portions, and wherein aplurality of closed magnetic circuits of the magnetic flux are formed inthe magnetic leg portions and the bases, and a magnetic resistance of atleast a smallest closed magnetic circuit from among the plurality ofclosed magnetic circuits is homogeneous.

According to the electric power conversion circuit, the first and secondenergization control elements can control the timing for energizing theinductor and the multi-parallel magnetic-field cancellation typetransformer and a current flow in the circuit, and the multi-parallelmagnetic-field cancellation type transformer can transform a voltage(step up/down a voltage) and convert electric power.

The electric power conversion circuit further comprises an inductorwhose one end is connected to a positive electrode of the firstinput-output connecting terminal, and whose other end is connected to acommon terminal connecting to the plurality of coils of the themulti-parallel magnetic-filed cancellation type transformer.

According to the electric power conversion circuit, the inductor canreduce the ripple component of the input current generated when thecircuit is energized, so that the size of input-output capacitors can bereduced and the electric power conversion efficiency can be improved byreducing the power loss of switching elements. Further, the electricpower conversion circuit can prevent a sharp increase of the currentflowing through the coils even if the multi-parallel magnetic-fieldcancellation type transformer is magnetically saturated due to atemperature variation.

According to the electric power conversion circuit, the firstenergization control elements are a switching element, and the secondenergization control elements are a rectifying element.

Accordingly, the electric power conversion circuit can step up anapplied voltage.

According to the electric power conversion circuit, the firstenergization control elements are a rectifying element, and the secondenergization control elements are a switching element.

Accordingly, the electric power conversion circuit can step down anapplied voltage.

According to the electric power conversion circuit, the firstenergization control elements and the second energization controlelements are a switching element.

Accordingly, the electric power conversion circuit can step up/down anapplied voltage.

According to the electric power conversion circuit, the switchingelement is constituted by an IGBT.

Accordingly, the switching element constituted of the IGBT withstands ahigh voltage, so that the switching element can be provided in order tocontrol an automobile electric motor where a large amount of current isapplied.

According to the electric power conversion circuit, the switchingelement is constituted by a MOS-FET.

Accordingly, the switching element constituted by the MOS-FET can reducethe power loss of switching, so that the electric power conversioncircuit can improve the electric power conversion efficiency even if thecircuit is applied in a high frequency band.

According to the electric power conversion circuit, the switchingelement includes a flywheel diode.

Accordingly, the switching element including the flywheel diode canprevent damage to the electric power conversion circuit by providing apath of the current when an inductor is turned off. Accordingly, theelectric power conversion circuit allows the current to flow in bothdirections.

Accordingly, if the coils disposed in parallel increase in number, thetransformers of the present invention can prevent magnetic saturation ofthe core and reduce the size thereof and a core loss. Consequently, theelectric power conversion circuit can reduce the size thereof andimprove the electric power conversion efficiency.

Further, the transformers of the present invention can reduce thecurrent flowing through each coil, and prevent the core loss generatedin the core and the deterioration of electric power conversionefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are circuit diagrams of an electric power conversioncircuit of an embodiment of the present invention. FIG. 1C is a circuitdiagram of a conventional electric power conversion circuit.

FIG. 2 is a perspective view of a transformer wherein coils are disposedin parallel, and the magnetic flux is shown in a dot line.

FIG. 3A is a perspective view of the transformer. FIG. 3B is anequivalent circuit of the transformer.

FIG. 4 is waveforms showing a gate signal of switching elements andcurrent waveforms of the electric power conversion circuits of FIGS. 1Aand 1C during voltage step-up operation.

FIG. 5 is waveforms showing a gate signal of switching elements andcurrent waveforms of the electric power conversion circuits of FIGS. 1Aand 1C during voltage step-down operation.

FIG. 6 is a graph showing a ripple current characteristic with respectto two-parallel and three-parallel magnetic-field cancellation typetransformers during voltage step-up operation.

FIG. 7 is a graph showing power loss with respect to the two-paralleland three-parallel magnetic-field cancellation type transformers duringvoltage step-up operation.

FIG. 8 is a graph showing actual operational waveforms of thethree-parallel magnetic-field cancellation type transformer.

FIGS. 9A to 9D are schematic views of the three-parallel magnetic-fieldcancellation type transformers. FIGS. 9E and 9F are schematic views ofthe four-parallel magnetic-field cancellation type transformers.

FIG. 10 is a schematic view of the two-parallel magnetic-fieldcancellation type transformer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, embodiments of the present invention will be described withreference to drawings in detail. FIGS. 1A and 1B are a circuit diagramof an electric power conversion circuit. The electric power conversioncircuit of FIG. 1A includes a three-parallel magnetic-field cancellationtype transformer. The electric power conversion circuit of FIG. 1Bincludes a four-parallel magnetic-field cancellation type transformer.An electric power conversion circuit of FIG. 1C includes a conventionaltwo-parallel magnetic-field cancellation type transformer. Hereinafter,the operation of the electric power conversion circuit of the presentinvention will be described, compared with the operation of theconventional electric power conversion circuit whose description isschematically shown.

FIG. 1A shows an electric power conversion circuit 1, wherein, involtage step-up operation, a voltage applied to an input terminal (firstinput/output connecting terminal) is stepped up and supplied to anoutput terminal (second input/output connecting terminal), and involtage step-down operation, a voltage applied to an input terminal(second input/output connecting terminal) is stepped down and suppliedto an output terminal (first input/output connecting terminal). Namely,the electric power is converted in both ways. The electric powerconversion circuit 1 includes a reactor L1A (inductor), capacitors C1Aand C2A, a transformer Tr1 (multi-parallel magnetic-field cancellationtype transformer), a first arm A1 constituted by a plurality of firstenergizing control elements, more specifically, a plurality of switchingelements for switching, which are used in the voltage step-up operationof the embodiment, and a second arm A2 constituted by a plurality ofsecond energizing control elements, more specifically, a plurality ofswitching elements for switching, which are used in the voltagestep-down operation of the embodiment. When the voltage is stepped up ordown only in one direction, energizing control elements can be replacedwith diodes functioning as a rectifier.

The input terminal is connected to a power supply (not shown) such as abattery and an electric generator, where a power supply voltage isapplied. The voltage applied to the input terminal is an input voltage.

A stepped-up/stepped-down input voltage is output from the outputterminal as an output voltage.

The reactor L1A accumulates and discharges magnetic energy when an inputvoltage is stepped up and stepped down respectively. The reactor L1A isdisposed between the transformer Tr1 and the positive electrode of theinput terminals.

By switching on and off the first arm A1 and the second arm A2, thecapacitors C1A and C2A repeatedly charge and discharge an electriccharge. The capacitors C1A and C2A are constituted of, for example, aceramic capacitor or a film capacitor in the embodiment.

The transformer Tr1 includes cores (iron core) about which a pluralityof coils are wound. The three-parallel magnetic-field cancellation typetransformer Tr1 is connected to the reactor L1A in the embodiment.According to the three-parallel magnetic-field cancellation typetransformer, a piece of magnetic flux is generated from a plurality ofcoils wound and disposed in parallel with each other when the currentflows through the plurality of coils. The direction of the magnetic fluxis substantially opposite to each other, whereby counteracting eachother (canceling each other out). According to the core of thetransformer Tr1, a part where the coil is wound is called as a magneticleg portion and another part where the coil is not wound is called as abase. Hereinafter, the transformer Tr1 will be described in detail withreference to FIGS. 2 to 3.

As shown in FIG. 2, the transformer Tr1 includes three magnetic legportions (α, β, γ) where the coils (a, b, c) are wound respectively.When each current (i1, i2, i3) flows through coils (a, b, c), magneticflux (Φ1, Φ2, Φ3) is generated respectively. In any couple selected fromamong of the pieces of the magnetic flux (Φ1, Φ2, Φ3) generated in thetransformer Tr1, the direction of the magnetic flux is opposite to eachother. More specifically, the direction of the magnetic flux (Φ1, Φ2) isopposite to each other. The direction of the magnetic flux (Φ2, Φ3) isopposite to each other. Further, the direction of the magnetic flux (Φ1,Φ3) is opposite to each other.

In FIG. 2, a closed magnetic circuit (loop) of the magnetic flux (Φ1,Φ2, Φ3) is shown in a dashed line. A pair of coils wound on the magneticleg portions α and γ generates a large closed magnetic circuit. Smallclosed magnetic circuits are generated from a pair of coils wound on themagnetic leg portions α and β as well as a pair of coils wound on themagnetic leg portions β and γ when the current flows.

The transformer Tr1 has a gap g at the magnetic leg portion β. The gap gallows the magnitude of the magnetic flux to be adjusted, so that themagnetic flux Φ1 and Φ2 is cancelled out with each other, the magneticflux Φ2 and Φ3 is cancelled out with each other, and the magnetic fluxΦ1 and Φ3 is cancelled out with each other. The gap g may as well rangeapproximately from several microns to several millimeters. An insulationsheet and the like can be interposed in the gap g. Cores of variousshapes will be described later. The explanation of operation returns toFIG. 1.

The first arm A1 is constituted by three switching elements (switchesSW1A, SW2A, and SW3A) and used for switching to step up an inputvoltage. According to the embodiment, the switching elements connectedin parallel are constituted by switches including a flywheel diode. Theswitching elements may as well be semiconductor devices such as aninsulated gate bipolar transistor (IGBT) and a metal oxide semiconductorfield effect transistor (MOS-FET). When the switching elements areconstituted of MOS-FETs, a parasitic diode of the MOS-FET may as well beused in place of the fly-wheel diode. Further, the flywheel diode may aswell be connected in parallel with the MOS-FETs. When the electric powerconversion circuit 1 is applied only for the voltage step-up operation,the second arm A2 which is not used for switching can be replaced withdiodes.

The second arm A2 is constituted by three switching elements (switchesSW5A, SW6A, and SW7A) and applied for switching when an input voltage isstepped down. According to the embodiment, the switching elementsconnected in parallel are constituted of switches including the flywheeldiode. The switching elements may as well be semiconductor devices suchas IGBTs and MOS-FETs. When the switching elements are constituted ofMOS-FETs, a parasitic diode of the MOS-FET can be applied in place ofthe fly-wheel diode. Further, the flywheel diode may as well beconnected in parallel with the MOS-FETs. When the electric powerconversion circuit 1 is applied only for the voltage step-downoperation, the second arm A1 which is not used for switching can bereplaced with the diodes.

An electric power conversion circuit 1A shown in FIG. 1B includes afour-parallel magnetic-field cancellation type transformer Tr2, a firstarm A3 and a second arm A4 which have four switching elementsrespectively. The transformer Tr2 is an alternating three-parallelmagnetic-filed cancellation type transformer Tr1 of the electric powerconversion circuit 1 shown in FIG. 1A. The first arm A3 and the secondarm A4 are the alternate first arm A1 and the second arm A2 whichinclude three switching elements. More specifically, each arm isconstituted by switching elements whose number is equal to the number ofcoils disposed in parallel.

Further, FIG. 1C shows an electric power conversion circuit 101including the conventional two-parallel magnetic-field cancellation typetransformer wherein a voltage applied to an input terminal is steppedup/down and supplied to an output terminal to be output. The electricpower conversion circuit includes a reactor L1, capacitors C1C and C2C,a transformer TrJ (two-parallel magnetic-field cancellation typetransformer), a first arm a1, and a second arm a2. The same elements aredesignated as the same references shown in FIG. 1A, and therebyduplicated descriptions are omitted.

The transformer TrJ (two-parallel magnetic-field cancellation typetransformer) includes two coils, wherein the direction of the magneticflux from the coils is opposite to each other.

The first arm a1 is constituted by two switching elements (switches SW1Cand SW2C) and used for switching when an input voltage is stepped up.According to the embodiment, the switching elements connected inparallel are constituted of switches including a flywheel diode. Theswitching elements may as well be semiconductor devices such as IGBTsand MOS-FETs. When the electric power conversion circuit 101 is usedonly for the voltage step-up operation, the second arm a2 which is notused for switching can be replaced with diodes.

The second arm a2 is constituted by two switching elements (switchesSW5C and SW6C) and used for switching to step down an input voltage.According to the embodiment, the switching elements connected inparallel are constituted by switches including the flywheel diode. Theswitching elements may as well be constituted by semiconductor devicessuch IGBTs and MOS-FETs. When the electric power conversion circuit 101is applied only for the voltage step-down operation, the second arm a1which is not used for switching can be replaced with diodes.

The switching operation of the first arm A1 and the second arm A2 willbe described with reference to FIGS. 4 and 5. The switching of the firstarm A1 and the second arm A2 is performed by a duty control. In FIGS. 4and 5, the switching of the first arm A1 and the second arm A2 will bedescribed, compared with the switching of the first arm a1 and thesecond arm a2 of the electric power conversion circuit 101 including theconventional two-parallel magnetic-field cancellation type transformershown in FIG. 1C. The switching of the first arm A3 and the second armA4 is substantially the same as that of the first arm A1 and the secondarm A2 shown in FIGS. 4 and 5. Accordingly, the duplicated descriptionsare omitted.

At first, the switching of the first arm A1 in voltage step-up operationwill be described with reference to FIG. 4. FIG. 4 shows waveforms ofON/OFF control signal for the first arm A1 constituted of the switchesSW1A, SW2A, and SW3A of FIG. 1A, an electric current waveform (shown ina solid line) of the reactor L1A of FIG. 1, and an electric currentwaveform (shown in the solid line) of the capacitor C2A of FIG. 1 wherevoltage step-up operation is performed by the switching of the first armA1. Further, FIG. 4 shows waveforms of ON/OFF control signal for thefirst arm a1 constituted by the switches SW1C and SW2C in FIG. 1C, anelectric current waveform (shown in dotted line) of the reactor L1C inFIG. 1C, and an electric current waveform (shown in the dotted line) ofthe capacitor C2C in FIG. 1C where the voltage step-up operation isperformed by the switching of the first arm a1.

In FIG. 4, one cycle is a period from ON state when the switch SW1A isswitched on to OFF state when the switch SW1A is switched off. FIG. 4shows a time period 7 from the time when the switch SW1C of the firstarm a1 is switched on to the time when the switch SW2C of the first arma1 is switched off (more specifically, period when both of the switchesSW1C and SW2C of the first arm a1 are kept switching on). Further, FIG.4 shows a time period 1 from the time when the switch SW1A of the firstarm A1 is switched on to the time when the switch SW3A of the first armA1 is switched off. Moreover, FIG. 4 shows a time period 2 from the timewhen the switch SW3A is switched off to the time when the switch SW2A isswitched on.

Subsequently, FIG. 4 indicates a time period 3 from the time when theswitch SW2A of the first arm A1 is switched on to the time when theswitch SW1A of the first arm A1 is switched off. FIG. 4 shows a timeperiod 8 from the time when the switch SW2C of the first arm a1 isswitched on to the time when the switch SW1A of the first arm A1 and theswitch SW1C of the first arm a1 are switched off (more specifically,during the period when the switches SW1A and SW1C are switched on). FIG.4 shows a time period 4 from the time when both the switch SW1A of thefirst arm A1 and the switch SW1C of the first arm a1 are switched off tothe time when the switch SW3A of the first arm A1 is switched on.

Further, FIG. 4 indicates a time period 5 from the time when the switchSW3A of the first arm A1 is switched on to the time when the switch SW2Aof the first arm A1 is switched off. FIG. 4 shows a time period 6 fromthe time when the switch SW2A of the first arm A1 is switched off to thetime when both the switch SW1A of the first arm A1 and the switch SW1Cof the first arm a1 are switched on.

As shown in FIG. 4, the one cycle for switching the first arm A1 in thevoltage step-up operation is divided into six periods from the timeperiods 1 to 6. The ripples (peak-to-peak) of the electric currentwaveforms of the reactor L1A and the capacitor C2A are reduced withrespect to the switching of the first arm A1, compared with theswitching of the conventional first arm a1. The frequency of the currentflowing through the reactor L1A (or the capacitor C2A) can be raised byincreasing the number of the switches disposed in parallel. Accordingly,the slope of the current flowing through the reactor L1A is reduced to alow gradient. In the embodiment, the frequency of the current can be 1.5times greater, compared with the conventional circuit.

Next, the switching of the second arm A2 in voltage step-down operationwill be described with reference to FIG. 5. FIG. 5 shows waveforms ofON/OFF control signal for the second arm A2 constituted by the switchesSW5A, SW6A, and SW7A in FIG. 1A, an electric current waveform (shown ina solid line) of the reactor L1A in FIG. 1, and an electric currentwaveform (shown in the solid line) of the capacitor C2A in FIG. 1 wherevoltage step-down operation is performed by the switching of the secondarm 2A. Further, FIG. 5 shows waveforms of ON/OFF control signal for thesecond arm a2 constituted by the switches SW5C and SW6C of FIG. 1C, anelectric current waveform (shown in dotted line) of the reactor L1C inFIG. 1C, and an electric current waveform (shown in the dotted line) ofthe capacitor C2C in FIG. 1C where the voltage step-down operation isperformed by the switching of the second arm a2.

In FIG. 5, one cycle of switching is a period from ON state when theswitch SW5A is switched on to OFF state when the switch SW5A is switchedoff. FIG. 5 shows a time period 7′ from the time when the switch SW5C ofthe second arm a2 is switched on to the time when the switch SW6C of thesecond arm a2 is switched off (more specifically, period when both theswitches SW5C and SW6C of the second arm a2 are kept switching on).Further, FIG. 5 shows a time period 1′ from the time when the switchSW5A of the second arm A2 is switched on to the time when the switchSW7A of the second arm A2 is switched off. Moreover, FIG. 5 shows a timeperiod 2′ from the time when the switch SW7A of the second arm A2 isswitched off to the time when the switch SW6A of the second arm A2 isswitched on.

Subsequently, FIG. 5 shows a time period 3′ from the time when theswitch SW6A of the second arm A2 is switched on to the time when theswitch SW5A of the second arm A2 is switched off. FIG. 5 shows a timeperiod 8′ from the time when the switch SW6C of the second arm a2 isswitched on to the time when both the switch SW5A of the second arm A2and the switch SW5C of the second arm a2 are switched off (morespecifically, during the period when the switches SW5A and SW5C are keptswitching on). FIG. 5 shows a time period 4′ from the time when both theswitch SW5A of the second arm A2 and the switch SW5C of the second arma2 are switched off to the time when the switch SW6A of the second armA2 is switched on.

Further, FIG. 5 shows a time period 5′ from the time when the switchSW7A of the second arm A2 is switched on to the time when the switchSW6A of the second arm A2 is switched off. FIG. 5 shows a time period 6′from the time when the switch SW6A of the second arm A2 is switched offto the time when both the switch SW5A of the second arm A2 and theswitch SW5C of the second arm a2 are switched on.

As shown in FIG. 5, the one cycle for switching the second arm A2 in thevoltage step-down operation is divided into six time periods from thetime periods 1′ to 6′. The ripples (peak-to-peak) of the currentwaveforms of the reactor L1A and the capacitor C2A are reduced withrespect to the switching of the second arm A2, compared with theswitching of the conventional second arm a2. The frequency of thecurrent flowing through the reactor L1A (or the capacitor C2A) can beraised by increasing the number of the switches disposed in parallel. Inthe embodiment, the frequency of the current can be 1.5 times greater,compared with the conventional circuit.

In the periods 7 and 8 of the voltage step-up operation, the switchesSW1C and SW2C are kept switching on. The switching of the switches SW1Cand SW2C disposed in parallel allows an input voltage to be stepped up,whereby providing an output voltage two times higher than the inputvoltage. In the periods 7′ and 8′ of the voltage step-down operation,the switches SW5C and SW6C of the second arm a2 are kept switching on.The switching of the switches SW5C and SW6C disposed in parallel allowsthe input voltage to be stepped down, whereby providing an outputvoltage 0.5 to 1.0 times lower than the input voltage. However, sincethe impedance of the electric power conversion circuit 1 is low, a largeamount of current flows through the inductor. Accordingly, the currentramps up in the periods, so that the ripple is outstandingly increased.In the periods of the voltage step-up operation, where the switching ofthree switches in parallel are simultaneously turned on, the threeswitches allows the input voltage to be stepped up, whereby providing anoutput voltage four times higher than the input voltage. However, as isthe same case where the two switches disposed in parallel are applied inorder to provide the voltage two times higher than the input voltage,the three switches disposed in parallel have the same problem as theincrease of the ripple.

Preferably, the number of switches disposed in parallel should bechanged in accordance with a desired voltage step-up rate with respectto the electric power conversion circuit 1.

Further, FIGS. 6 to 10 show operational comparison between the electricpower conversion circuit 1 and the electric power conversion circuit101, and between the three-parallel magnetic-field cancellation typetransformer Tr1 (hereinafter, simply referred to as a three-paralleltransformer) and the conventional two-parallel magnetic-fieldcancellation type transformer TrJ (hereinafter referred to as atwo-parallel transformer), as well as the operational waveforms of thetransformer Tr1

FIG. 6 shows the relationship of the voltage step-up rate to a ripplecurrent of the reactor L1 and electric power conversion efficiency. FIG.7 shows the relationship of the voltage step-up rate to the power lossof magnetic components (reactor and transformer). FIG. 8 is an actualoperational waveforms of the transformer Tr1. FIG. 9 shows theembodiments of the transformer applied for the circuit including threeswitches disposed in parallel or four switches disposed in parallel.FIG. 10 shows a configuration view of the transformer applied to thecircuit including two switches disposed in parallel.

As shown in FIG. 6, if the voltage step-up rate is two times withrespect to the voltage step-up operation, the ripple current is reducedto 0 A in the circuit including two switches disposed in parallel. Ifthe voltage step-up rate is greater than two times, a measured value 2MC of the ripple current is remarkably increased in the circuit.Further, if the voltage step-up rate exceeds two times, a measuredefficiency 2M, which is an electric power conversion efficiency of thecircuit including two switches disposed in parallel, significantlydrops. On the other hand, if the voltage step-up rate is 1.5 and 3times, a measured value 3 CM of the ripple current is 0 A in the circuitincluding three switches disposed in parallel. Further, even if thevoltage step-up rate exceeds 1.5 and 3 times, the measured value 3 CM ofthe ripple current is not significantly increased in the circuit. If thevoltage step-up rate exceeds two and three times, a measured efficiency3M, which indicates the electric power conversion efficiency of thecircuit including three switches disposed in parallel, does not dropsignificantly.

As shown in FIG. 7, a huge power loss W of magnetic components isgenerated in the circuit including two switches disposed in parallelduring the voltage step-up operation. The power loss is due to a highamplitude of the ripple current in the circuit including two switchesdisposed in parallel, compared with the circuit including three switchesdisposed in parallel.

As shown in FIG. 8, when a slight variation is generated in the currentflowing through each coil, the transformer Tr1 (three-parallel) canreduce the difference in direct current component of the current flowingthrough each coil by controlling the duty ratio of on-off period of theswitches, whereby providing a stable voltage step-up operation.Accordingly, by reducing the difference in the direct current componentof the stationary current flowing through the coils, the transformer Tr1can cancel out the magnetic fields in the core. More specifically, byreducing the difference in the direct current component of the currentflowing through the coils, the magnitude of magnetic flux generated fromthe coils can be equalized for cancellation. Consequently, thetransformer Tr1 can prevent the magnetic saturation of the core.

To be specific, the transformer Tr1 effectively performs thecancellation of magnetic flux generated from the coils in which a directcurrent flows, and reduces the variation of the stationary current (thedifference in the direct current component of the current flowingthrough each coil) by adjusting a winding ratio (preferably, turns ratioof each coil is 1:1), a length of magnetic path, and a cross section ofthe magnetic path. Accordingly, the transformer Tr1 can prevent themagnetic saturation and reduce the size thereof.

Further, various types of magnetic-field-cancellation-type transformersof a different shape (core shape) will be described with reference toFIGS. 9A to 9F, and 10.

FIGS. 9A to 9D show three-parallel magnetic-field cancellation typetransformers Tr1 (transformers Tr1a, Tr1b, Tr1c,and Tr1d). FIGS. 9E and9F show four-parallel magnetic-field cancellation type transformers Tr2(transformers Tr2e and Tr2e). FIG. 10 shows a conventional two-parallelmagnetic-field cancellation type transformer TrJ (transformer TrJ1).

As shown in FIGS. 9A to 9C, three-parallel magnetic-field cancellationtype transformers (Tr1a, Tr1b, Tr1c, and Tr1d) include a plurality ofcoils M which generate the magnetic flux during energization, and a coreCO having three magnetic leg portions G (G1A, G2A, G3A, G1B, G2B, GB3,G1C, G2C, and G3C) where the coil M is wound, and bases B which fix thethree magnetic leg portions.

The multi-parallel magnetic-field cancellation type transformer(three-parallel type) includes the plurality of coils wound on themagnetic leg portions G. Accordingly, the direction of the magnetic fluxgenerated from the plurality of coils is opposite to each other. Aplurality of closed-magnetic circuits of the magnetic flux are formed atthe magnetic leg portions G and the bases B. At least, a magneticresistance of the minimum closed magnetic circuit (loop) out of theplurality of closed magnetic circuits is homogeneous. The multi-parallelmagnetic-field cancellation type transformer (three-parallel type)includes the plurality of coils M connected in parallel which generatethe magnetic flux during energization, so that the magnetic path lengthof the closed magnetic circuit is homogeneous.

The multi-parallel magnetic-field cancellation type transformer (thethree-parallel and four-parallel types) is constructed to equalize themagnetic path length in order to obtain the homogeneous magneticresistance of the closed magnetic circuits, whereby balancing themagnetic flux density distribution and preventing the magneticsaturation. In this case, the magnetic resistance Rm is calculated asfollows; Rm=1/μ·L/A (magnetic permeability: μ, length of magnetic path:L, cross section of magnetic path: A). If the product of the magneticpermeability and the cross section of magnetic path is constant in theformula described above, the homogeneous magnetic resistance can beobtained in accordance with the equal length of magnetic path.

FIG. 9A shows the three-parallel magnetic-field cancellation typetransformer (transformer Tr1a) in which a base Ba of a core 9COa isformed in a circular shape. Magnetic leg portions GA1, GA2, and GA3 areextended from the center of the circular base to the circumference anddisposed at regular intervals apart on the circumference.

FIG. 9B shows the three-parallel magnetic-field cancellation typetransformer (transformer Tr1b), in which a base Bb of a core 9COb isformed in a regular polygonal shape (in the embodiment, in a regulartriangle). Magnetic leg portions GB1, GB2 and GB3 are extended from thecenter of the regular polygon to the sides (apexes) and disposed atregular intervals apart on the sides.

FIG. 9C shows the three-parallel magnetic-field cancellation typetransformer (transformer Tr1c), in which there is a gap GP formed at amagnetic leg portion GC2 which is the center between three magnetic legportions.

FIG. 9D shows the three-parallel magnetic-field cancellation typetransformer (transformer Tr1d) in which bases Bd1 and Bd2 of a core 9COdare formed in a circular shape (or a regular triangle) and disposed inparallel with each other. Three magnetic leg portions GD1, GD2, and GD3formed in a cylindrical shape are formed vertically to the bases Bd1 andBd2 and disposed between the bases Bd1 and Bd2. The three magnetic legportions GD1, GD2, and GD3 are disposed at regular intervals apart.

Further, FIG. 9E shows the four-parallel magnetic-field cancellationtype transformer (transformer Tr2e) which includes a plurality of coilsM which generate magnetic flux which being energized, and a core 9COehaving four magnetic leg portions GE1, GE2, GE3, and GE4 on which theplurality of coils M are wound respectively, and a base Be for fixingthe four magnetic leg portions. Further, the base Be of the core 9COe isformed in a regular polygon (in the embodiment in a regular square). Thefour magnetic leg portions GE1, GE2, GE3, and GE4 are extended from thecenter of the regular polygon to the sides (apexes) and fixed at regularintervals apart on the sides.

FIG. 9F shows a four-parallel magnetic-field cancellation typetransformer (transformer Tr2f) in which bases Bf1 and Bf2 of a core 9COfare formed on two planes which are disposed in parallel with each other.Four magnetic leg portions GF1, GF2, GF3, and GF4 are disposedvertically to the planes and formed in a cylindrical shape. Further, thefour magnetic leg portions GF1, GF2, GF3, and GF4 are disposed atregular intervals apart. On one plane, the base Bf1 is constituted byonly a part where one ends of four magnetic leg portions are mutuallyjoined, and on the other plane, the base Bf2 is constituted by only apart where the other ends of the four magnetic leg portions are mutuallyjoined.

FIG. 10 shows a conventional multi-parallel magnetic-field cancellationtype transformer TrJ1 which includes two coils Mj which generatemagnetic flux which being energized, and a core COj having a magneticleg portion Gj on which the two coils Mj are wound, and a base Bj forfixing the magnetic leg portion Gj. The two coils wound on the magneticleg portion Gj are disposed in such a manner that the direction of themagnetic flux generated from the two coils is opposite to each other.The multi-parallel magnetic-field cancellation type transformergenerates a plurality of closed magnetic circuits of the magnetic fluxat the magnetic leg portion Gj and the base Bj. Accordingly, a magneticresistance of the closed magnetic circuits is homogeneous.

The transformers Tr1 and Tr2 can adjust the amount of magnetic fluxgenerated in the closed magnetic circuit, so that the transformers cancancel out the direct current magnetic flux generated from each coil atthe electric power conversion. Accordingly, if the number of the coilsdisposed in parallel increases, the transformers can prevent magneticsaturation of the core, and reduce the size thereof and a core loss.Further, according to the transformers Tr1 and Tr2, since the coils Mare connected in parallel, the thickness of the coils M can be reduced,whereby improving the latitude of design of the coils and spaceefficiency.

Since the magnetic leg portions GA1, GA2 and GA3 of the transformer Tr1aare connected to the circular base Ba and disposed at regular intervalsapart on the circumference, the magnetic path length of each closedmagnetic circuit can be homogeneous, which makes magnetic resistanceconstant. Consequently, the transformer Tr1a can cancel out directcurrent magnetic flux generated from each coil M at the electric powerconversion. Even if the coils disposed in parallel increase in number,the transformer Tr1a can prevent the magnetic saturation of the core andreduce the core loss therein. According to the transformer Tr1b, sincethe magnetic leg portions GB1, GB2, and GB3 are connected to the base Bbformed in a regular polygonal shape and disposed at regular intervals onthe sides of the base, the magnetic path length of each closed magneticcircuit can be homogeneous, which makes magnetic resistance constant.Consequently, the transformer Tr1b can cancel out direct currentmagnetic flux generated from each coil M at the electric powerconversion. Even if the coils disposed in parallel increase in number,the transformer Tr1b can prevent the magnetic saturation of the core andreduce the core loss therein.

In any one of the combinations of the magnetic flux (Φ1, Φ2, Φ3)generated from the coils wound on the three magnetic leg portions GC1,GC2, and GC3, the direction of the magnetic flux in the transformer Tr1cis opposite to each other to be cancelled out. Since there is the gap GPformed at the magnetic leg portion GC2 which is the center between threemagnetic leg portions, so that the magnitude of magnetic flux can beadjusted so as to make magnetic resistance constant. Consequently, thetransformer Tr1c can cancel out direct current magnetic flux generatedfrom each coil M at the electric power conversion. Even if the coilsconnected in parallel increase in number, the transformer Tr1c canprevent the magnetic saturation of the core and reduce the core losstherein.

Since the two bases Bd1 and Bd2 are respectively formed on two planesdisposed in parallel with each other, and three magnetic leg portionsGD1, GD2, and GD3 formed in a cylindrical shape are vertically disposedbetween the bases Bd1 and Bd2, the magnetic path length of each closedmagnetic circuit can be homogeneous, which makes magnetic resistanceconstant. Consequently, the transformer Tr1d can cancel out directcurrent magnetic flux generated from each coil M at the electric powerconversion. Even if the number of the coils disposed in parallelincreases, the transformer Tr1d can prevent the magnetic saturation ofthe core and reduce the core loss therein.

On one plane of the transformer Tr2e, the base Bf1 of the core 9COf isconstituted by only a part where one ends of four magnetic leg portionsare mutually joined, and on the other plane, the base Bf2 of the core9COf is constituted by only a part where the other ends of the fourmagnetic leg portions are mutually joined. Accordingly, the transformerTr2e can provide a lightweight core, compared with the base having aflat plane.

In view of the electric power conversion circuit including thetransformer Tr1 or Tr2, the first arm A1(A3) and the second arm A2 (A4)can control energization timing for the inductor L1A and the transformerTr1 (Tr2) of multi-parallel magnetic-field cancellation type, and acurrent flow in the electric power conversion circuit, so that themulti-parallel magnetic-field cancellation type transformer cantransform (step up/down) a voltage and convert electric power. Even ifthe number of the coils increases, the multi-parallel magnetic-fieldcancellation type transformer Tr1 (Tr2) can prevent the magneticsaturation of the core and reduce the weight thereof and the core loss.Consequently, the electric power conversion circuit 1 can reduce theweight thereof and provide a high conversion efficiency.

The embodiments of the present invention are not limited but can bemodified. For example, in the embodiments, the multi-parallelmagnetic-field cancellation type transformer Tr1b is formed in a squaretriangle. However, other regular polygon (regular pentagon, regularhexagon) can be applied. In the embodiments, the inductor is connectedto the positive electrode of the input/output terminal of the electricpower conversion circuit 1. However, the connecting point is notlimited. The inductor can be connected to the negative electrode of theinput/output terminal of the electric power conversion circuit 1.

1. An electric power conversion circuit which converts an electric powerby transforming an input voltage and includes a first input-outputconnecting terminal and a second input-output terminal, the electricpower conversion circuit comprising: a multi-parallel magnetic-filedcancellation type transformer; an inductor whose one end is connected toa positive electrode of the first input-output connecting terminal, andwhose other end is connected to a common terminal connecting to theplurality of coils of the multi-parallel magnetic-filed cancellationtype transformer; a plurality of first energization control elementswhose one ends are connected to the plurality of coils respectively, andwhose other ends are connected to a negative electrode of the firstinput-output connecting terminal; and a plurality of second energizationcontrol elements whose one ends are connected to the plurality of coilsrespectively, and whose other ends are connected to a positive electrodeof the second input-output connecting terminal.
 2. The electric powerconversion circuit according to claim 1, wherein the multi-parallelmagnetic-filed cancellation type transformer further comprises: aplurality of coils, each of which generates magnetic flux whenenergized; and a core comprising a plurality of magnetic leg portionsabout which the coils are wound; and a base for fixing the plurality ofthe magnetic leg portions, wherein the direction of magnetic fluxgenerated from the plurality of coils is opposite to each other in anycouple selected from among the pieces of the magnetic flux, so that themagnetic flux is cancelled out with each other, and wherein a pluralityof closed magnetic circuits of the magnetic flux are formed in themagnetic leg portions and the base, and a magnetic resistance of atleast a smallest closed magnetic circuit from among the plurality ofclosed magnetic circuits is homogeneous.
 3. The electric powerconversion circuit according to claim 1, wherein the multi-parallelmagnetic-filed cancellation type transformer further comprises: aplurality of coils, each of which generates magnetic flux whenenergized; and a core comprising: three magnetic leg portions aboutwhich the coils are wound; and a base for fixing the three magnetic legportions, wherein the three magnetic leg portions are disposed atregular intervals in one direction, and the direction of the magneticflux generated from the plurality of coils wound on the three magneticleg portions is opposite to each other in any couple selected from amongthe pieces of magnetic flux, so that the magnetic flux is cancelled outwith each other, and there is a gap at the magnetic leg portion formedat the center between the three magnetic leg portions, and wherein aplurality of closed magnetic circuits of the magnetic flux are formed inthe magnetic leg portions and the bases, and a magnetic resistance of atleast a smallest closed magnetic circuit from among the plurality ofclosed magnetic circuits is homogeneous.
 4. An electric power conversioncircuit which converts an electric power by transforming an inputvoltage and includes a first input-output connecting terminal and asecond input-output terminal, the electric power conversion circuitcomprising: a multi-parallel magnetic-filed cancellation typetransformer; a plurality of first energization control elements whoseone ends are connected to the plurality of coils respectively, and whoseother ends are connected to a negative electrode of the firstinput-output connecting terminal; and a plurality of second energizationcontrol elements whose one ends are connected to the plurality of coilsrespectively, and whose other ends are connected to a positive electrodeof the second input-output connecting terminal.
 5. The electric powerconversion circuit according to claim 3, wherein the multi-parallelmagnetic-filed cancellation type transformer further comprises: aplurality of coils, each of which generates magnetic flux whenenergized; and a core comprising: three magnetic leg portions aboutwhich the coils are wound; and a base for fixing the three magnetic legportions, wherein the three magnetic leg portions are disposed atregular intervals in one direction, and the direction of the magneticflux generated from the plurality of coils wound on the three magneticleg portions is opposite to each other in any couple selected from amongthe pieces of magnetic flux, so that the magnetic flux is cancelled outwith each other, and there is a gap at the magnetic leg portion formedat the center between the three magnetic leg portions, and wherein aplurality of closed magnetic circuits of the magnetic flux are formed inthe magnetic leg portions and the bases, and a magnetic resistance of atleast a smallest closed magnetic circuit from among the plurality ofclosed magnetic circuits is homogeneous.
 6. The electric powerconversion circuit according to claim 3, further comprising an inductorwhose one end is connected to a positive electrode of the firstinput-output connecting terminal, and whose other end is connected to acommon terminal connecting to the plurality of coils of themulti-parallel magnetic-filed cancellation type transformer.
 7. Theelectric power conversion circuit according to claim 1, wherein thefirst energization control elements are a switching element, and thesecond energization control elements are a rectifying element.
 8. Theelectric power conversion circuit according to claim 1, wherein thefirst energization control elements are a rectifying element, and thesecond energization control elements are a switching element.
 9. Theelectric power conversion circuit according to claim 1, wherein thefirst energization control elements and the second energization controlelements are a switching element.
 10. The electric power conversioncircuit according to claim 6, wherein the switching element isconstituted by an IGBT.
 11. The electric power conversion circuitaccording to claim 6, wherein the switching element is constituted by aMOS-FET.
 12. The electric power conversion circuit according to claim 6,wherein the switching element includes a flywheel diode.